U.S. patent application number 17/739899 was filed with the patent office on 2022-08-25 for notched gate structure fabrication.
The applicant listed for this patent is Taiwan Semiconductor Manufacturing Co., Ltd.. Invention is credited to Che-Cheng Chang, Chang-Yin Chen, Chih-Han Lin.
Application Number | 20220270928 17/739899 |
Document ID | / |
Family ID | 1000006318617 |
Filed Date | 2022-08-25 |
United States Patent
Application |
20220270928 |
Kind Code |
A1 |
Chen; Chang-Yin ; et
al. |
August 25, 2022 |
Notched Gate Structure Fabrication
Abstract
A method includes providing a substrate having a channel region,
forming a gate stack layer over the channel region, forming a
patterned hard mask over the gate stack layer, etching a top
portion of the gate stack layer through openings in the patterned
hard mask with a first etchant, etching a middle portion and a
bottom portion of the gate stack layer with a second etchant that
includes a passivating gas. A gate stack is formed with a
passivation layer deposited on sidewalls of the gate stack. The
method also includes etching the gate stack with a third etchant,
thereby removing a bottom portion of the passivation layer and
recessing a bottom portion of the gate stack.
Inventors: |
Chen; Chang-Yin; (Taipei
City, TW) ; Chang; Che-Cheng; (New Taipei City,
TW) ; Lin; Chih-Han; (Hsinchu City, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Taiwan Semiconductor Manufacturing Co., Ltd. |
Hsin-Chu |
|
TW |
|
|
Family ID: |
1000006318617 |
Appl. No.: |
17/739899 |
Filed: |
May 9, 2022 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
17099613 |
Nov 16, 2020 |
11328962 |
|
|
17739899 |
|
|
|
|
16161833 |
Oct 16, 2018 |
10840153 |
|
|
17099613 |
|
|
|
|
62690697 |
Jun 27, 2018 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 29/66545 20130101;
H01L 21/82385 20130101; H01L 21/823821 20130101; H01L 29/66795
20130101; H01L 29/4966 20130101; H01L 21/3065 20130101; H01L
27/0924 20130101; H01L 29/42376 20130101; H01L 21/823814 20130101;
H01L 29/517 20130101; H01L 29/66553 20130101; H01L 29/1033
20130101; H01L 21/30608 20130101; H01L 21/3086 20130101 |
International
Class: |
H01L 21/8238 20060101
H01L021/8238; H01L 29/66 20060101 H01L029/66; H01L 29/51 20060101
H01L029/51; H01L 29/49 20060101 H01L029/49; H01L 21/308 20060101
H01L021/308; H01L 27/092 20060101 H01L027/092; H01L 29/10 20060101
H01L029/10; H01L 21/306 20060101 H01L021/306; H01L 21/3065 20060101
H01L021/3065; H01L 29/423 20060101 H01L029/423 |
Claims
1. A method, comprising: providing a substrate having a channel
region; forming a gate stack layer over the channel region; forming
a patterned hard mask over the gate stack layer; etching a top
portion of the gate stack layer through openings in the patterned
hard mask with a first etchant; etching a middle portion and a
bottom portion of the gate stack layer with a second etchant that
includes a passivating gas, thereby forming a gate stack with a
passivation layer deposited on sidewalls of the gate stack; and
etching the gate stack with a third etchant, thereby removing a
bottom portion of the passivation layer and recessing a bottom
portion of the gate stack.
2. The method of claim 1, wherein the passivating gas is an
oxygen-containing gas, and the passivation layer includes an
oxide.
3. The method of claim 1, wherein the passivating gas is a
nitrogen-containing gas, and the passivation layer includes a
nitride.
4. The method of claim 1, wherein the passivating gas contains a
mixture of oxygen and nitrogen, and the passivation layer includes
an oxynitride.
5. The method of claim 1, wherein prior to the etching of the gate
stack with the third etchant, the bottom portion of the passivation
layer is thinner than a top portion of the passivation layer.
6. The method of claim 5, wherein after the etching of the gate
stack with the third etchant, the top portion of the passivation
layer remains.
7. The method of claim 1, wherein after the etching of the gate
stack with the third etchant, a width of the bottom portion of the
gate stack is reduced.
8. The method of claim 1, wherein the gate stack is a dummy gate
stack, the method further comprising: after the etching of the gate
stack with the third etchant, replacing the gate stack with a metal
gate stack.
9. The method of claim 1, wherein the second etchant includes a
mixture of HBr and the passivating gas, and the third etchant
includes HBr but free of the passivating gas.
10. The method of claim 1, wherein the channel region is in a form
of a fin protruding from the substrate.
11. A method, comprising: providing a semiconductor substrate
having a first channel region and a second channel region; forming
a gate material layer over the first and second channel regions;
patterning the gate material layer, thereby forming a first gate
stack over the first channel region and a second gate stack over
the second channel region; and laterally recessing bottom portions
of the first and second gate stacks with an etchant in an etch
reactor, wherein the etch reactor is configured to exhibit a higher
etching strength of the etchant towards the second gate stack than
towards the first gate stack.
12. The method of claim 11, wherein the etch reactor is configured
to flow the etchant with a higher flow rate towards the second gate
stack than towards the first gate stack.
13. The method of claim 11, wherein the etch reactor is configured
to apply a stronger radio frequency (RF) field strength above the
second gate stack than above the first gate stack.
14. The method of claim 11, wherein the semiconductor substrate is
a wafer, the first channel region is located in a center region of
the wafer, and the second channel region is located in a peripheral
region of the wafer.
15. The method of claim 11, wherein the patterning of the gate
material layer includes applying a passivating gas towards the
first and second gate stacks, thereby forming passivation layers on
sidewalls of the first and second gate stacks.
16. The method of claim 15, wherein the etchant is free of the
passivating gas.
17. The method of claim 11, wherein the etch reactor is a plasma
etch reactor, and the patterning of the gate material layer and the
laterally recessing of the bottom portions of the first and second
gate stacks are in-situ in the plasma etch reactor.
18. A method of semiconductor device fabrication, comprising:
providing a semiconductor wafer; forming a first plurality of
channel regions in a center area of the semiconductor wafer and a
second plurality of channel regions in an edge area of the
semiconductor wafer; forming a dielectric layer over the first and
second pluralities of channel regions; patterning the dielectric
layer, thereby forming a first plurality of dummy gates over the
first plurality of channel regions and a second plurality of dummy
gates over the second plurality of channel regions; and performing
a lateral etching process to the first and second pluralities of
dummy gates by applying different etchant flow rates to the center
and edge areas, thereby forming the first and second pluralities of
dummy gates with bottom portions narrower than respective top
portions.
19. The method of claim 18, wherein a maximum variation of widths
of the bottom portions of the first and second pluralities of dummy
gates is less than 10%.
20. The method of claim 18, wherein the patterning of the
dielectric layer also forms passivation layers on sidewalls of the
first and second pluralities of dummy gates, and the performing of
the lateral etching process also removes bottom portions of the
passivation layers.
Description
PRIORITY DATA
[0001] This is a continuation of U.S. patent application Ser. No.
17/099,613, filed Nov. 15, 2020, which is a continuation of U.S.
patent application Ser. No. 16/161,833, filed Oct. 16, 2018, now
issued U.S. Pat. No. 10,840,153, which claims priority to U.S.
Provisional Patent Application Ser. No. 62/690,697 filed on Jun.
27, 2018, herein incorporated by reference in its entirety.
BACKGROUND
[0002] The semiconductor integrated circuit (IC) industry has
experienced exponential growth. Technological advances in IC
materials and design have produced generations of ICs where each
generation has smaller and more complex circuits than the previous
generation. In the course of IC evolution, functional density
(i.e., the number of interconnected devices per chip area) has
generally increased while geometry size (i.e., the smallest
component (or line) that can be created using a fabrication
process) has decreased. This scaling down process generally
provides benefits by increasing production efficiency and lowering
associated costs. Such scaling down has also increased the
complexity of processing and manufacturing ICs.
[0003] One advancement in some IC design and fabrication has been
the developing of a notched gate structure that has notched
sidewalls at its bottom instead of substantially vertical
sidewalls. One of the benefits of the notched gate structure is its
enlarging the distance between bottoms of adjacent gate structures,
which effectively mitigates metal gate protrusion during a
replacement gate or "gate-last" process. However, there are
challenges to maintain the uniformity of notched gate structure
profiles across a wafer. For example, a gate patterning process may
generate an etch rate difference and a critical dimension (CD) bias
between a center region and an edge region of a wafer, causing not
only a center-to-edge gate structure dimension variation but also
greatly deteriorating a chip yield in an edge region. Although
existing approaches in notched gate structure formation have been
generally adequate for their intended purposes, they have not been
entirely satisfactory in all respects. Accordingly, there exists a
need for improvements in this area.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] The present disclosure is best understood from the following
detailed description when read with the accompanying figures. It is
emphasized that, in accordance with the standard practice in the
industry, various features are not drawn to scale and are used for
illustration purposes only. In fact, the dimensions of the various
features may be arbitrarily increased or reduced for clarity of
discussion.
[0005] FIG. 1A shows a top view of a semiconductor structure with
transistors formed in different regions with a notched gate
structure fabrication process, according to aspects of the present
disclosure.
[0006] FIGS. 1B, 1C, and 1D show cross-sectional views of the
semiconductor structure in FIG. 1A, in accordance with an
embodiment.
[0007] FIGS. 2A and 2B show a flow chart of a method for forming
the semiconductor structure shown in FIGS. 1A-1D, according to
aspects of the present disclosure.
[0008] FIGS. 3, 4, 5, 6, 7, 8, 9, 10A, 10B, 12A, 12B, 13A, 13B,
14A, 14B, 15A, 15B, 16A, and 16B illustrate cross-sectional views
of a semiconductor structure during a fabrication process according
to the method of FIGS. 2A-2B, in accordance with an embodiment.
[0009] FIGS. 11A and 11B show exemplified plasma process chambers
used in a fabrication process according to the method of FIGS. 2A
and 2B, according to aspects of the present disclosure.
DETAILED DESCRIPTION
[0010] The following disclosure provides many different
embodiments, or examples, for implementing different features of
the provided subject matter. Specific examples of components and
arrangements are described below to simplify the present
disclosure. These are, of course, merely examples and are not
intended to be limiting. For example, the formation of a first
feature over or on a second feature in the description that follows
may include embodiments in which the first and second features are
formed in direct contact, and may also include embodiments in which
additional features may be formed between the first and second
features, such that the first and second features may not be in
direct contact. In addition, the present disclosure may repeat
reference numerals and/or letters in the various examples. This
repetition is for the purpose of simplicity and clarity and does
not in itself dictate a relationship between the various
embodiments and/or configurations discussed.
[0011] Further, spatially relative terms, such as "beneath,"
"below," "lower," "above," "upper" and the like, may be used herein
for ease of description to describe one element or feature's
relationship to another element(s) or feature(s) as illustrated in
the figures. The spatially relative terms are intended to encompass
different orientations of the device in use or operation in
addition to the orientation depicted in the figures. The apparatus
may be otherwise oriented (rotated 90 degrees or at other
orientations) and the spatially relative descriptors used herein
may likewise be interpreted accordingly. Still further, when a
number or a range of numbers is described with "about,"
"approximate," and the like, the term is intended to encompass
numbers that are within +/-10% of the number described, unless
otherwise specified. For example, the term "about 5 nm" encompasses
the dimension range from 4.5 nm to 5.5 nm.
[0012] The present disclosure is generally related to semiconductor
devices and fabrication methods. More particularly, the present
disclosure is related to providing a notched gate structure and a
gate fabrication technique that maintains the uniformity of notched
gate structure profile at a wafer scale. In the forming of field
effect transistors (FETs), the critical dimension (CD) of gate
stacks affects many operating parameters of integrated circuits,
such as speed performance and power consumption of a circuit. There
is also a concern that the diminishing CD and closer base distances
between adjacent gate stacks may aggravate device shorting caused
by metal material leakage from a defect gate stack during a
replacement gate or "gate-last" process, termed as "metal gate
protrusion." Notched gate structure has been developed as a way to
reduce the chance of metal gate protrusion from occurring. Besides,
the notched gate structure reduces effective gate stack CDs and
enlarges distance from the bottom of a gate stack to other FETs
features, therefore mitigating possible shorting caused by metal
gate protrusion. In some cases, different regions of a wafer suffer
from etch rate differences and CD bias across the wafer during
notched gate structure formation. As an example, gate stack
structures in edge regions of a wafer are sometimes found under
etched at the bottom of gate stacks, while the ones in center
regions are sometimes found over etched. This might cause circuit
defects and chip yield deterioration. An object of the present
disclosure is to maintain the uniformity of notched gate structure
profile across the whole wafer by applying different etch rates to
different regions of the wafer during the notched gate structure
formation.
[0013] FIG. 1A illustrates a top view of a semiconductor device (or
semiconductor structure) 100. FIG. 1B illustrates a cross-sectional
view of the device 100 along the B-B line of FIG. 1A. FIG. 1C
illustrates a cross-sectional view of the device 100 along the C-C
line of FIG. 1A. FIG. 1D illustrates a cross-sectional view of the
device 100 along the D-D line of FIG. 1A.
[0014] Referring to FIG. 1A, the device 100 can be a wafer, part of
a wafer, or a substrate with fabricated features thereon. In the
illustrated embodiment, the device 100 is a semiconductor wafer
(e.g., a silicon wafer). A wafer usually exhibits a disk shape with
a radius r.sub.0. The diameter (2r.sub.0) of the disk may range
from O-200 mm (O-8 inch) to O-450 mm (O-18 inch), such as a O-300
mm (O-12 inch) wafer in a specific example. From a top view, the
device 100 can be divided into multiple regions, such as edge
regions and center regions, depending on a distance to a center of
the device 100. In the illustrated embodiment, the device 100 is
divided into a center region I within radius r.sub.1 and an edge
region (or peripheral region) II outside of radius r.sub.1. In a
furtherance of the embodiment, r.sub.1 is about 71% of r.sub.0,
resulting in the region I and region II having substantially equal
areas from a top view.
[0015] The device 100 may be an intermediate device fabricated
during processing of an integrated circuit (IC) that may comprise
static random access memory (SRAM) and/or logic circuits, passive
components such as resistors, capacitors, and inductors, and active
components such as p-type FETs (pFETs), n-type FETs (nFETs),
FinFETs, metal-oxide semiconductor field effect transistors
(MOSFET), and complementary metal-oxide semiconductor (CMOS)
transistors, bipolar transistors, high voltage transistors, high
frequency transistors, other memory cells, and combinations
thereof. Furthermore, the various features including transistors,
gate stacks, active regions, isolation structures, and other
features in various embodiments of the present disclosure are
provided for simplification and ease of understanding and do not
necessarily limit the embodiments to any types of devices, any
number of devices, any number of regions, or any configuration of
structures or regions.
[0016] In the illustrated embodiment, the device 100 includes a
substrate 102, a plurality of fins 104 protruding out of the
substrate 102 including the fin 104a in the edge region II and the
fin 104b in the center region I, and a plurality of gate structures
112 disposed over the fins 104 including the gate stack 112a over
the fin 104a and the gate stack 112b over the fin 104b. In some
embodiments, the gate structures 112 are also referred to as gate
stacks 112 or gate stack layers 112. The fins 104 are arranged
lengthwise along the X direction, and the gate stacks 112 are
arranged lengthwise along the Y direction which is generally
perpendicular to the X direction. Further, the fins 104 are
generally parallel to each other, and the gate stack 112 are
generally parallel to each other. Each portion of the gate stacks
112 engages the respective fins 104 to form individual field effect
transistors (FET), which includes a channel region 114 inside the
fin 104 and covered by the gate structure 112, such as the channel
region 114a in the edge region II and the channel region 114b in
the center region I.
[0017] Referring to FIGS. 1B, 1C, and 1D collectively, the device
100 may further include a dielectric liner layer 103 on sidewalls
of the fins 104, an isolation structure 106 over the substrate 102
and between the fins 104, gate spacers 160 on sidewalls of the gate
stack 112, and an interlayer dielectric (ILD) layer 166. Each gate
stack 112 includes a high-k dielectric layer 108 and a conductive
layer 110 over the high-k dielectric layer 108. The conductive
layer 110 includes one or more layers of metallic materials.
Therefore, each gate stack 112 is also referred to as a high-k
metal gate (or HK MG) 112. The gate stacks 112 may further include
an interfacial layer (not shown) under the high-k dielectric layer
108. Each gate stack 112 is disposed over the top surface 170 of
the respective fin 104 and covers its sidewalls. The bottom of the
gate stack 112 is also laying above the isolation structure
106.
[0018] Referring to FIG. 1C, the gate stack 112 has a portion above
the top surface 170 of the fin 104, denoted as the upper portion
116-1, and a portion below the top surface 170 of the fin 104,
denoted as the lower portion 116-2. In some embodiments, the upper
portion 116-1 is also referred to as a top portion 116-1, and the
lower portion 116-2 is also referred to as a bottom portion 116-2.
The position of the top surface 170 of the fin 104 is marked by a
dashed line in FIG. 1C for the sake of clarity in the comparisons.
The top portion 116-1 has a top width w.sub.0 and a bottom width
w.sub.1. The top width w.sub.0 is larger than or at least equal to
the bottom width w.sub.1 in various embodiments. In the illustrated
embodiment, the top portion 116-1 has substantially vertical
sidewalls; therefore, the widths w.sub.0 and w.sub.1 are about the
same, ranging from about 16 nm to about 240 nm, such as about 145
nm. Contrastively, the lower portion 116-2 has sidewalls titled
inwardly. A tilted sidewall and the top surface of the isolation
structure 106 (as well as the top surface of the substrate 102)
form an angle O ranging from about 45 degrees to about 85 degrees
in some embodiments, such as about 80 degrees. The top portion
116-1 has a height ho ranging from about 20 nm to about 500 nm in
some embodiments. The bottom portion 116-2 has a height h.sub.1,
which is less than h.sub.0 (h.sub.1<h.sub.0) in some
embodiments. In the illustrated embodiment, h.sub.1 is smaller than
50 nm. The bottom width w.sub.1 of the top portion 116-1 is also
the top width of the bottom portion 116-2. The middle width w.sub.2
of the bottom portion 116-2 is measured at half height of h.sub.1
(h.sub.1/2). In various embodiments, w.sub.2 is smaller than
w.sub.1 by about 0.1 nm to about 15 nm. The bottom width w.sub.3 of
the bottom portion 116-2 is further shrunk, such as smaller than
w.sub.1 by about 0.1 nm to about 30 nm. In a specific example,
w.sub.0 and w.sub.1 are both about 145 nm, w.sub.2 is about 141 nm
(about 4 nm less than w.sub.1), and w.sub.3 is about 137 nm (about
8 nm less than w.sub.1). In another example, w.sub.3 is about 10%
to about 100% of w.sub.1. The gate stack 112 has a smaller
effective CD in the lower portion 116-2 than in the upper portion
116-1. The tilted sidewalls surround the gate stack 112's notched
portion. In the illustrated embodiment, the sidewall of the gate
stack 112 starts being notched inwardly at about the same height of
the top surface 170 of the fin 104. While in some other
embodiments, the sidewalls of the gate stack 112 may start being
notched inwardly above or below the top surface 170 of the fin 104.
It is sometimes found that the bottom width w.sub.3 of the lower
portion 116-2 suffers a large variation across the wafer. For
example, a bottom width w.sub.3' in the edge region II may be equal
to or up to about 50% larger than a bottom width w.sub.3 in the
center region I. In some examples, in the edge region II, a bottom
width w.sub.3' may be even larger than a width w1 measured at the
height h.sub.1, a scenario in which a metal gate protrusion would
be relatively easier to occur. The notched gate structure
fabrication method to be discussed in further details later on can
effectively maintain the uniformity of the bottom width w.sub.3
across different regions of the wafer.
[0019] Referring again to FIGS. 1B, 1C, and 1D collectively, the
components of the device 100 are further described below. The
substrate 102 is a silicon substrate in the present embodiment.
Alternatively, the substrate 102 may comprise another elementary
semiconductor, such as germanium; a compound semiconductor
including silicon carbide, gallium nitride, gallium arsenide,
gallium phosphide, indium phosphide, indium arsenide, and indium
antimonide; an alloy semiconductor including silicon germanium,
gallium arsenide phosphide, aluminum indium phosphide, aluminum
gallium arsenide, gallium indium arsenide, gallium indium
phosphide, and gallium indium arsenide phosphide; or combinations
thereof. In another embodiment, the substrate 102 includes indium
tin oxide (ITO) glass.
[0020] The fins 104 may comprise one or more semiconductor
materials such as silicon, germanium, silicon carbide, gallium
arsenide, gallium phosphide, indium phosphide, indium arsenide,
indium antimonide, silicon germanium, gallium arsenide phosphide,
aluminum indium phosphide, aluminum gallium arsenide, gallium
indium arsenide, gallium indium phosphide, and gallium indium
arsenide phosphide. In an embodiment, the fins 104 may include
alternately stacked layers of two different semiconductor
materials, such as layers of silicon and silicon germanium
alternately stacked. The fins 104 may additionally include dopants
for improving the performance of the device 100. For example, the
fins 104 may include n-type dopant(s) such as phosphorus or
arsenic, or p-type dopant(s) such as boron or indium.
[0021] The liner layer 103 may include silicon nitride (e.g.,
Si.sub.3N.sub.4), and may be deposited using chemical vapor
deposition (CVD) such as low-pressure CVD (LPCVD) or
plasma-enhanced CVD (PECVD), atomic layer deposition (ALD), or
other suitable methods.
[0022] The isolation structure 106 may comprise silicon oxide,
silicon nitride, silicon oxynitride, fluoride-doped silicate glass
(FSG), a low-k dielectric material, and/or other suitable
insulating material. The isolation structure 106 may be shallow
trench isolation (STI) features. The isolation structure 106 may be
deposited using CVD such as flowable CVD, or other suitable
methods.
[0023] The high-k dielectric layer 108 may include one or more
high-k dielectric materials (or one or more layers of high-k
dielectric materials), such as hafnium silicon oxide (HfSiO),
hafnium oxide (HfO.sub.2), alumina (Al.sub.2O.sub.3), zirconium
oxide (ZrO.sub.2), lanthanum oxide (La.sub.2O.sub.3), titanium
oxide (TiO.sub.2), yttrium oxide (Y.sub.2O.sub.3), strontium
titanate (SrTiO.sub.3), or a combination thereof. The high-k
dielectric layer 108 may be deposited using CVD, ALD and/or other
suitable methods.
[0024] The conductive layer 110 includes one or more metal layers,
such as work function metal layer(s), conductive barrier layer(s),
and metal fill layer(s). The work function metal layer may be a
p-type or an n-type work function layer depending on the type (PFET
or NFET) of the device. The p-type work function layer comprises a
metal with a sufficiently large effective work function, selected
from but not restricted to the group of titanium nitride (TiN),
tantalum nitride (TaN), ruthenium (Ru), molybdenum (Mo), tungsten
(W), platinum (Pt), or combinations thereof. The n-type work
function layer comprises a metal with sufficiently low effective
work function, selected from but not restricted to the group of
titanium (Ti), aluminum (Al), tantalum carbide (TaC), tantalum
carbide nitride (TaCN), tantalum silicon nitride (TaSiN), titanium
silicon nitride (TiSiN), or combinations thereof. The metal fill
layer may include aluminum (Al), tungsten (W), cobalt (Co), and/or
other suitable materials. The conductive layer 110 may be deposited
using methods such as CVD, PVD, plating, and/or other suitable
processes.
[0025] The gate spacers 160 may comprise a dielectric material,
such as silicon oxide, silicon nitride, silicon oxynitride, silicon
carbide, other dielectric material, or combinations thereof, and
may comprise one or multiple layers of material. The gate spacers
160 may be deposited using CVD, ALD and/or other suitable
methods.
[0026] The ILD layer 166 may comprise tetraethylorthosilicate
(TEOS) oxide, un-doped silicate glass, or doped silicon oxide such
as borophosphosilicate glass (BPSG), fused silica glass (FSG),
phosphosilicate glass (PSG), boron doped silicon glass (BSG),
and/or other suitable dielectric materials. The ILD layer 166 may
be formed by PECVD (plasma enhanced CVD), FCVD (flowable CVD), or
other suitable methods.
[0027] The device 100 further includes source/drain (S/D) features
162 disposed over the fins 104. Generally, S/D features 162 are
disposed on each of the fins 104 in their respective S/D regions.
In one embodiment, the S/D features 162 disposed on the fin 104a
include p-type doped silicon germanium, and the S/D features 162
disposed on the fin 104b include n-type doped silicon.
[0028] The device 100 further includes one or more dielectric
layers, such as a protective dielectric layer 168 which may
comprise a nitride such as silicon nitride for protecting the ILD
layer 166, and a contact etch stop layer (CESL) 164 disposed over
the S/D features 162. The CESL 164 may also be disposed over the
isolation structure 106. The CESL 164 may comprise silicon nitride,
silicon oxynitride, silicon nitride with oxygen (O) or carbon (C)
elements, and/or other materials; and may be formed by CVD, PVD,
ALD, or other suitable methods.
[0029] FIGS. 2A and 2B illustrate a flow chart of a method 200 for
forming the device 100 in accordance with an embodiment. The method
200 is merely an example, and is not intended to limit the present
disclosure beyond what is explicitly recited in the claims.
Additional operations can be provided before, during, and after the
method 200, and some operations described can be replaced,
eliminated, or moved around for additional embodiments of the
method. The method 200 is described below in conjunction with FIGS.
3-16B. FIGS. 3-10B and 12A-16B illustrate various cross-sectional
views of the semiconductor device 100 during fabrication steps
according to the method 200. Specifically, FIGS. 3-9 illustrate a
cross-sectional view of the device 100 along the D-D line of FIG.
1A. FIGS. 10A, 12A, 13A, 14A, 15A, and 16A illustrate
cross-sectional views of the device 100 along the B-B line of FIG.
1A. FIGS. 10B, 12B, 13B, 14B, 15B, and 16B illustrate
cross-sectional views of the device 100 along the C-C line of FIG.
1A. FIGS. 11A and 11B illustrate various exemplary plasma
processing chambers suitable for using in certain operations of the
method 200.
[0030] At operation 202, the method 200 (FIG. 2A) provides, or is
provided with, a device structure 100 having a substrate 102, such
as shown in FIG. 3. The various materials for the substrate 102
have been discussed above with reference to FIGS. 1A-1D. In various
embodiments, the substrate 102 is a wafer, such as a silicon wafer,
and may include one or more epitaxially grown semiconductor layers
in its upper portion. Operation 202 also includes forming a
patterned mask 101 over the substrate 102. The patterned mask 101
may be formed using one or more photolithography processes,
including double-patterning or multi-patterning processes.
Generally, double-patterning or multi-patterning processes combine
photolithography and self-aligned processes, allowing patterns to
be created that have, for example, pitches smaller than what is
otherwise obtainable using a single, direct photolithography
process. For example, in one embodiment, a sacrificial layer is
formed over the substrate 102 and patterned using a
photolithography process. Spacers are formed alongside the
patterned sacrificial layer using a self-aligned process. The
sacrificial layer is then removed, and the remaining spacers, or
mandrels, become the patterned mask 101. The patterned mask 101 may
include silicon oxide, silicon nitride, photoresist, or other
suitable materials in various embodiments.
[0031] Operation 202 further includes etching the substrate 102
using the patterned mask 101 as an etch mask, thereby forming the
fins 104, such as shown in FIG. 4. The patterned mask 101 is
removed thereafter. The etching process can include dry etching,
wet etching, reactive ion etching (RIE), and/or other suitable
processes. For example, a dry etching process may implement an
oxygen-containing gas, a fluorine-containing gas (e.g., CF.sub.4,
SF.sub.6, CH.sub.2F.sub.2, CHF.sub.3, and/or C.sub.2F.sub.6), a
chlorine-containing gas (e.g., Cl.sub.2, CHCl.sub.3, CCl.sub.4,
and/or BCl.sub.3), a bromine-containing gas (e.g., HBr and/or
CHBr.sub.3), an iodine-containing gas, other suitable gases and/or
plasmas, and/or combinations thereof. For example, a wet etching
process may comprise etching in diluted hydrofluoric acid (DHF);
potassium hydroxide (KOH) solution; ammonia; a solution containing
hydrofluoric acid (HF), nitric acid (HNO.sub.3), and/or acetic acid
(CH.sub.3COOH); or other suitable wet etchant.
[0032] At operation 204, the method 200 (FIG. 2A) forms a liner
layer 103 over sidewalls of the fins 104. In the illustrated
embodiment, the liner layer 103 is deposited over top and sidewalls
of the fins 104 and over a top surface of the substrate 102, such
as shown in FIG. 5. To further the illustrated embodiment, the
liner layer 103 includes silicon nitride (e.g., Si.sub.3N.sub.4),
and may be deposited using LPCVD, PECVD, ALD, or other suitable
methods. The liner layer 103 may be deposited to a thickness of 1
to 5 nm, such as 3 nm. Operation 204 may, operationally, further
include applying an anisotropic etching process to the liner layer
103. The anisotropic etching process is designed to selectively
etch the liner layer 103 but does not etch the substrate 102. The
operation 204 may removes portions of the liner layer 103 from the
top surface of the substrate 102, thereby exposing the substrate
102 between the fins 104 (not shown). The portion of the liner
layer 103 on the sidewalls of the fins 104 remains substantially
un-etched due to the highly directional etching. Further, the top
surface of the fins 104 may or may not be exposed by this
anisotropic etching process. In an embodiment where the liner layer
103 includes silicon nitride, the operation 204 may employ a remote
O.sub.2/N.sub.2 discharge with a fluorine-containing gas such as
CF.sub.4, NF.sub.3, or SF.sub.6, and may additionally include
hydrogen (H.sub.2) or CH.sub.4. Various other methods of
selectively etching the liner layer 103 are possible.
[0033] At operation 206, the method 200 (FIG. 2A) forms an
isolation structure 106 over the liner layer 103 and filling spaces
between the fins 104, such as shown in FIG. 6. The operation 206
may include a variety of processes such as deposition (e.g., FCVD),
annealing, chemical mechanical planarization (CMP), and etching
back. For example, the operation 206 may deposit a flowable
dielectric material over the substrate 102 and filling spaces
between the fins 104. In some embodiments, the deposition of the
flowable dielectric material includes introducing a
silicon-containing compound and an oxygen-containing compound that
react to form a flowable dielectric material, thereby filling the
gaps. The material for the isolation structure 106 may include
undoped silicate glass (USG), fluoride-doped silicate glass (FSG),
phosphosilicate glass (PSG), borophosphosilicate glass (BPSG), or
other suitable insulating material. Subsequently, the operation 214
treats the flowable material with some annealing processes to
convert the flowable dielectric material into a solid dielectric
material. The annealing processes may include dry annealing or wet
annealing with a temperature ranging from 400 to 550.degree. C.
Thereafter, the operation 206 performs one or more CMP processes
and/or etching back processes to recess the isolation structure
106.
[0034] At operation 208, the method 200 (FIG. 2A) recesses the
isolation structure 106 and the liner layer 103 to expose upper
portions of the fins 104, such as shown in FIG. 7. The operation
208 may employ one or more wet etching, dry etching, reactive ion
etching, or other suitable etching methods in various embodiments.
For example, the isolation structure 106 and the liner layer 103
may be recessed in a single etch process. In alternative
embodiments, the isolation structure 106 is recessed using a first
etch process, and subsequently, the liner layer 103 is recessed
using a second etch process.
[0035] At operation 210, the method 200 (FIG. 2A) forms a gate
stack layer 112 over the fins 104 and filling spaces between the
fins 104, such as shown in FIG. 8. The gate stack layer 112 will be
subsequently patterned to form a gate stack, which will be used to
define and form the source/drain regions. In the illustrated
embodiment, the gate stack to be patterned from the gate stack
layer 112 is a dummy gate stack and will be replaced by a final
gate stack in a gate-last process. In some embodiments, the gate
stack to be patterned from the gate stack layer 112 is the final
gate stack, for example, in a gate-first process.
[0036] In some embodiments, the gate stack layer 112 includes a
dummy gate dielectric layer and a dummy gate electrode layer. The
dummy gate dielectric layer is formed over the exposed fins 104.
The dummy gate dielectric layer may be formed by thermal oxidation,
CVD, sputtering, or any other methods known and used in the art for
forming a dummy gate dielectric layer. In one embodiment, the dummy
gate dielectric layer is formed of the same material as the
isolation structure 106. In other embodiments, the dummy gate
dielectric layer may be made of one or more suitable dielectric
materials such as silicon oxide (e.g., SiO.sub.2), silicon nitride
(e.g., Si.sub.3N.sub.4), silicon oxynitride (e.g., SiON), low-k
dielectrics such as carbon doped oxides, extremely low-k
dielectrics such as porous carbon doped silicon dioxide, a polymer
such as polyimide, the like, or a combination thereof. In other
embodiments, the dummy gate dielectric layer includes dielectric
materials having a high dielectric constant (k value), for example,
greater than 3.9. The materials may include metal oxides such as
HfO.sub.2, HfZrO.sub.x, HfSiO.sub.x, HfTiO.sub.x, HfAlO.sub.x, TiN,
the like, or a combination thereof. Subsequently, the dummy gate
electrode layer is formed over the dummy gate dielectric layer. In
some embodiments, the dummy gate electrode layer is a conductive
material and may be selected from a group comprising
poly-crystalline silicon (poly-Si), poly-crystalline
silicon-germanium (poly-SiGe), silicon nitride (e.g.,
Si.sub.3N.sub.4), metallic nitrides, metallic silicides, and
metallic oxides. In an embodiment, the dummy gate electrode layer
may be deposited by PVD, CVD, sputter deposition, or other
techniques known and used in the art for depositing conductive
materials. The top surface of the dummy gate electrode layer
usually has a non-planar top surface and may be planarized in one
or more CMP processes after it is deposited.
[0037] At operation 212, the method 200 (FIG. 2A) forms a hard mask
layer 120 over the gate stack layer 112. The hard mask layer 120
may include one or more patterning layers, such as a first hard
mask layer 122 and a second hard mask layer 124, such as shown in
FIG. 9. Each of the hard mask layers 122 and 124 may include one or
more layers of dielectric material such as silicon oxide, silicon
nitride, and/or silicon oxynitride. For example, the first hard
mask layer 122 may be an oxide layer (e.g., silicon oxide) and the
second hard mask layer 124 may be a nitride layer (e.g., silicon
nitride). The first hard mask layer 122 and the second hard mask
layer 124 may be deposited through a process such as CVD or other
suitable methods. The first hard mask layer 122 may have a
thickness from about 10 .ANG.to about 50 .ANG.and the second hard
mask layer 124 may have a thickness from about 150 .ANG.to about
850 .ANG..
[0038] Operation 212 further includes patterning the hard mask
layer 120 by photolithography and etching processes, such as shown
in FIGS. 10A and 10B, which show cross-sectional views of the
device 100 cut along the B-B line and the C-C line of FIG. 1A,
respectively. The photolithography and etching processes may first
pattern the second hard mask layer 124, then pattern the first hard
mask layer 122 using the patterned second hard mask layer 124 as an
etching mask. An exemplary photolithography process may include
forming a photoresist (not shown) over the second hard mask layer
124. A lithographic exposure is performed on the device 100 that
exposes selected regions of the photoresist to radiation. The
exposure causes a chemical reaction to occur in the exposed regions
of the photoresist. After exposure, a developer is applied to the
photoresist. The developer dissolves or otherwise removes either
the exposed regions in the case of a positive resist development
process or the unexposed regions in the case of a negative resist
development process. Suitable positive developers include TMAH
(tetramethyl ammonium hydroxide), KOH, and NaOH, and suitable
negative developers include solvents such as n-butyl acetate,
ethanol, hexane, benzene, and toluene. After the photoresist is
developed, the exposed portions of the second hard mask layer 124
may be removed by an etching process, such as wet etching, dry
etching, Reactive Ion Etching (RIE), ashing, and/or other etching
methods. Subsequently, a pattern formed in the etched second hard
mask layer 124 is transferred to the first hard mask layer 122 by
selectively etching through openings in the patterned second hard
mask layer 124, resulting in a patterned hard mask layer 122. The
patterned hard mask layers 122 and 124 are denoted collectively as
a patterned hard mask 120. After etching, the photoresist may be
removed.
[0039] At operation 214, the method 200 (FIG. 2B) patterns the gate
stack layer 112 using the patterned hard mask 120 as an etching
mask. In an embodiment, the operation 214 includes first patterning
the various layers of the gate stack layer 112 including the dummy
gate electrode layer and the dummy gate dielectric layer to form
gate stacks with substantially vertical sidewalls, and subsequently
laterally etching the bottom portion of gate stacks to form notched
bases. In a particular embodiment, the operation 214 uses a dry
etch process, such as plasma etching, reactive-ion etching (RIE),
or other suitable anisotropic etching methods. Relatively speaking,
the merits of implementing a dry etch process are due mainly to its
simplicity of controlling the plasmas and its result of producing
more repeatable results than other processes, such as a wet etch
method. Many plasma parameters, such as gas pressure, chemistry,
and the source/biased power can be varied or modified during the
dry etch process to fine tune resulted gate stack sidewall
profile.
[0040] An exemplary plasma processing chamber (or plasma etch
reactor) 300 suitable for operation 214, according to various
embodiments of the present disclosure, is illustrated in FIG. 11A.
The plasma etch reactor chamber 300 includes a vacuum chamber 310.
The vacuum chamber 310 is in fluid communication with a vacuum
source 320 via a passage 322. The vacuum source 320 can include one
or more vacuum pumps. The vacuum source 320 is operable in
maintaining the interior of the vacuum chamber 310 at a suitable
low pressure (e.g., below 100 mTorr). The plasma etch reactor 300
also includes a chuck 330 for holding the device 100. As discussed
above, the device 100 can be divided into multiple regions, such as
a center region I and an edge region II surrounding the center
region I. In some embodiments, the chuck 330 is a cantilevered
electrostatic chuck, and the device 100 is positioned on the chuck
330 by an electrostatic clamp, a mechanical clamp, or other
clamping mechanism. The chuck 330 is conductive and electrically
coupled to a bias voltage source 332. The plasma etch reactor 300
further includes a dielectric top cover 334 with a plurality of
electrodes 336 mounted thereon. The dielectric top cover 334 and
the electrodes 336 may further be insulated by the insulation
members 340 from the side and bottom portions of the vacuum chamber
310. The electrodes 336, such as antennas or planar coils, are
powered by a suitable radio frequency (RF) power source 338 to
transmit RF energy into the vacuum chamber 310. Coupled with the
bias from the bias voltage source 332, the RF energy is capable of
transforming etchant gas inside the vacuum chamber 310 into
plasma.
[0041] Instead of using a gas ring or a gas showerhead to supply
etchant gas into the chamber, the plasma etch reactor 300 further
includes a plurality of gas injectors 342 spreading through the
space above the chuck 330, such as a central gas injector 342a and
peripheral gas injectors 342b. The gas injectors 342 provide
etchant gas to generate plasma within the vacuum chamber 310. In
some embodiments, the etchant gas is an inert gas, such as argon.
In some other embodiments, the etchant gas can be an inert gas,
oxygen, nitrogen, CF.sub.4, Cl.sub.2, HBr, and/or a combination
thereof. Each gas injector 342 may include one or more nozzles
capable of injecting gas downwardly or in a tilted angel.
Furthermore, each gas injector 342 is individually operable to
modulate etchant flow rate or completely shut off the fluid
communication with the vacuum chamber 310, such as by tuning a
valve associated with the respective gas injector. By applying
different etchant flow rate settings to gas injectors 342, the
etchant flow rate (or etchant concentration) directly above
different regions of the device 100 can vary. For example, by
setting a higher etchant flow rate to the peripheral gas injectors
342b than the central gas injector 342a, the etchant concentration
above the edge region II may become about 5% to about 20% higher
than the center region I. In a specific example, the edge region II
and the center region I have an etchant concentration ratio about
53%:47%. The higher etchant concentration in an edge region
compensates the etchant's relatively weaker etching capability away
from a center region, resulting in effective the same etch rates in
both edge and center regions. Therefore, introducing etchant
concentration regional variation instead of keeping a constant
etchant concentration is found effective in mitigating
center-to-edge etch bias and CD bias at a wafer scale. In various
other embodiments, the plasma etch reactor 300 is capable of
setting etchant concentration variation over more than two regions,
such as a gradient over three regions including an edge region, a
middle region, and a center region of the device 100.
[0042] The plasma etch reactor 300' as shown in FIG. 11B is similar
to the one shown in FIG. 11A. Therefore, reference numerals in FIG.
11A are repeated in FIG. 11B to show the same or similar features.
Furthermore, some descriptions of the same or similar features are
abbreviated or omitted by referring to the descriptions of the
plasma etch reactor 300 in FIG. 11A for the sake of simplicity. The
plasma etch reactor 300' has multiple groups of electrodes 336,
such as a central group of electrodes 336a, which is electrically
coupled to a first RF power source 338a, and an edge group of
electrodes 336b, which is electrically coupled to a second RF power
source 338b. The RF power sources 338a and 338b couple different
strength of RF energy into the central and edge groups of
electrodes, respectively. Therefore, the RF field strength varies
above different regions of the device 100. For example, the second
RF power source 338b may generate substantially more RF power than
the first RF power source 338a, resulting in a stronger RF field
above the edge regional II than above the center region I, which
enhances etchant's etching capability at edge regions. In other
embodiments, gas injectors 342 can also be adjusted together with
the RF power sources 338 to enhance etchant's etching capability in
targeted regions.
[0043] Referring back to FIG. 2B, the method 200 at operation 214
may include operations 214a, 214b, and 214c, which are further
discussed below. At operation 214a, the method 200 anisotropically
etch a top portion of the gate stack layer 112 using the patterned
hard mask 120 as an etching mask, such as shown in FIGS. 12A and
12B. The etching process may recess the top surface of the gate
stack layer 112 at a distance h ranging from about 1 nm to about 20
nm. The etching process may be a dry etching process performed
inside a plasma etch reactor similar to the ones illustrated above
in FIGS. 11A and 11B. The dry etching process includes the usage of
one or more etchants or a mixture of etchants. For example, the
etchant 130 may have the atoms of chlorine, fluorine, argon,
bromine, hydrogen, carbon, or a combination thereof. For example,
the etchant 130 may be a plasma containing a mixture of CF.sub.4
and Cl.sub.2 (i.e., CF.sub.4/Cl.sub.2 plasma).
[0044] In furtherance of the example, the etching process is
applied with an CF.sub.4/Cl.sub.2 flow rate between 0 and about 500
sccm, a gas pressure between 0 and about 60 mtorr, an RF power
between 0 and about 1000 W, and a bias voltage between 0 and about
200 V. In one embodiment, at operation 214a, the gas injectors 342
are set to maintain a substantial constant etchant flow rate across
different regions of the device 100. In yet another embodiment, the
operation 214a is optional and can be skipped.
[0045] At operation 214b, the method 200 (FIG. 2B) continues to
anisotropically etch the middle and bottom portions of the gate
stack layer 112 to form gate stacks, such as shown in FIGS. 13A and
13B. The etching process uses a top portion of the patterned gate
stack layer 112 formed in the previous operation 214a and the
patterned hard mask 120 collectively as an etching mask, resulting
in a plurality of gate stacks, such as gate stacks 112a and 112b.
The etching process is a selectively etching that does not
substantially damage the top surface 170 of the fins 104 and the
top surface of the isolation structure 106. The operation 214b may
include a dry etching process with an etchant 132 having the atoms
of chlorine, fluorine, bromine, oxygen, hydrogen, carbon, or a
combination thereof. For example, the etchant 132 may have a gas
mixture of Cl.sub.2, O.sub.2, a carbon-and-fluorine containing gas,
a bromine-and-fluorine containing gas, and a
carbon-hydrogen-and-fluorine containing gas. Specifically, the
etchant 132 includes at least one gas that can passivate exposed
sidewalls of the gate stacks 112a and 112b, such as O.sub.2 or a
mixture of O.sub.2 and N.sub.2. In one embodiment, the silicon
containing particles bombarded away during the etch process may
react with the passivation gas to generate silicon oxide or silicon
nitride containing particles that partially deposit on sidewalls of
the gate stacks 112a and 112b and form a passivation layer 128. The
passivation layer 128 protects sidewalls of the gate stack from
further etching by the etchant 132. The passivation layer 128 may
have a lower portion thinner than an upper portion, as its upper
portion is exposed to oxide and/or nitride particles in a longer
time than its lower portion. In one example, the etchant 132
includes O.sub.2 and the passivation layer 128 includes silicon
oxide. In another example, the etchant 132 includes NH.sub.3and the
passivation layer 128 includes silicon nitride. In yet another
example, the etchant 132 includes O.sub.2 and N.sub.2, and the
passivation layer 128 includes silicon oxynitride. In a specific
embodiment, the etchant 132 is a plasma containing a mixture of
Cl.sub.2, O.sub.2, CF.sub.4, BCl.sub.3, and CHF.sub.3. In another
embodiment, the etchant 132 is a plasma containing a mixture of HBr
and O.sub.2 (i.e., HBr/O.sub.2 plasma). The etching process may be
performed inside a plasma etch reactor similar to the ones
illustrated above in FIGS. 11A and 11B, with other parameters such
as a HBr flow rate less than about 500 sccm, a gas pressure less
than about 60 mtorr, an RF power less than about 1000 W, and a bias
voltage less than about 200 V. The operation 214b may be in-situ
with the operation 214a in the same plasma etch reactor. In one
embodiment, at operation 214b, the gas injectors 342 are set to
maintain a substantially constant etchant flow rate across
different regions of the device 100.
[0046] At operation 214c, the method 200 (FIG. 2B) etches the
bottom portion of the gate stack 112a and 112b, resulting in a
notched gate profile, such as shown in FIGS. 14A and 14B. The
operation 214c may include a dry etching process performed inside a
plasma etch reactor similar to the ones illustrated above in FIGS.
11A and 11B, but under a stronger bias voltage, higher RF power,
and/or higher gas pressure than in the operation 214b, which
modulates the etchant to exhibit stronger lateral etching
capability. The etching process is also a selectively etching that
does not substantially damage the top surface 170 of the fins 104
and the top surface of the isolation structure 106. The operation
214c may apply an etchant 134 having the atoms of chlorine,
fluorine, bromine, hydrogen, carbon, or a combination thereof. In
one embodiment, the etchant 134 is the same as the etchant 132 used
in the operation 214b but without passivation gases. In furtherance
of the embodiment, the etchant 134 is a plasma containing HBr
(i.e., HBr plasma), but free of O.sub.2, N.sub.2, or NH.sub.3. The
operation 214c may be in-situ with the operations 214a and 214b in
the same plasma etch reactor, with other parameters such as a HBr
flow rate between about 500 and about 1000 sccm, a gas pressure
between about 60 and about 90 mtorr, an RF power between about 1000
W and about 2000 W, and a bias voltage between about 200 V and
about 500 V. The etchant 134 has certain lateral etch rate toward
the passivation layer 128 covering sidewalls of the gate stacks
112a and 112b. The passivation layer 128 at its bottom portion is
removed by the etchant 134 earlier than its top portion due to its
relatively thinner thickness, therefore exposing the bottom
sidewalls of the gate stacks 112a and 112b while the top sidewalls
are still covered. The etchant 134 subsequently laterally etches
the exposed bottom sidewalls and form a notched gate structure
profile. The remaining passivation layer 128 protects the top
portion of the sidewalls from etching. The notched sidewalls may
exhibit a curvature surface profile in some embodiments, as
illustrated by the dotted line 140. The dimensions of the notched
gate stack profile have been discussed above with reference to
FIGS. 1A-1D.
[0047] If the gas injectors 342, at operation 214c, are set to
maintain a substantially constant etchant flow rate across
different regions of the device 100, the bottom width w.sub.3 of
the gate stacks may have a large variation across the wafer. For
example, a bottom width w.sub.3' in the edge region II may be about
2% to about 30% larger than a bottom width w.sub.3 in the center
region I. In the illustrated embodiment, by applying different
etchant flow rate settings to gas injectors 342, the etchant flow
rate (or etchant concentration) above different regions of the
device 100 becomes different. For example, the etchant
concentration above the edge region II of the substrate 102 may be
maintained at a level about 5% to about 20% higher than the center
region I. In a specific example, for a wafer with a center region I
and an edge region II having substantially equal areas from a top
view, a HBR plasma with a total flow rate 750 sccm is guided
through the gas injectors 342, with about 53% flow rate (about
427.5 sccm) guided towards the edge region II and about 47% flow
rate (about 322.5 sccm) guided towards the center region I. This
etchant concentration regional variation is helpful in mitigating
center-to-edge etch bias at a wafer scale and maintains
substantially the same etch rate of bottom portion of the gate
stacks in different regions across the wafer during notch
formation. As a result, the bottom width w.sub.3 and w.sub.3' are
kept substantially the same. In some embodiments, the plasma etch
reactor applies different RF power to generate different RF field
strength above the edge region II and the center region I to vary
the respective etchant's etch rates, as discussed above in
association with FIG. 11B. The RF power regional variation may be
applied alone at the operation 214c or applied together with the
etchant flow rate settings in gas injectors 342. Similarly, the RF
power regional variation is helpful in mitigating center-to-edge
etch bias at a wafer scale and maintains substantially the same
etch rate of bottom portion of the gate stacks in different regions
across the wafer during notch formation.
[0048] After operation 214, for two gate stacks 112a and 112b in
different regions but supposed to have substantially the same
bottom width, the respective bottom width w.sub.3' and w.sub.3 have
a maximum variation .DELTA.w less than 10% across the wafer, in
some embodiments. The maximum variation .DELTA.w is denoted as
.DELTA.w=w.sub.3' max-w.sub.3 min/(w.sub.3' max+w.sub.3 min)/2
[0049] where: w.sub.3' max is the maximum w.sub.3' measured in edge
region II; [0050] w.sub.3 min is the minimum w.sub.3 measured in
center region I; and [0051] (w.sub.3' max+w.sub.3 min)/2 represents
an average gate stack bottom width. In some embodiments, the bottom
width w.sub.3 and w.sub.3' have a maximum variation .DELTA.w less
than 5% across the wafer.
[0052] At operation 216, the method 200 (FIG. 2B) forms various
features in or over the fins 104, including gate spacers 160,
source/drain (S/D) features 162, a contact etch stop layer (CESL)
164, an interlayer dielectric (ILD) layer 166, and a protective
dielectric layer 168, such as shown in FIGS. 15A and 15B. The
operation 216 includes a variety of processes.
[0053] In a particular embodiment, the operation 216 forms the gate
spacers 160 on sidewalls of the gate stacks 112. The gate spacers
160 may comprise a dielectric material, such as silicon oxide,
silicon nitride, silicon oxynitride, silicon carbide, other
dielectric material, or combinations thereof, and may comprise one
or multiple layers of material. The gate spacers 160 may be formed
by depositing a spacer material as a blanket over the isolation
structure 106, the fins 104, and the dummy gate structures (not
shown). Then the spacer material is etched by an anisotropic
etching process. Portions of the spacer material on the sidewalls
of the dummy gate structures remain and become the gate spacers
160.
[0054] Then, the operation 216 forms the S/D features 162 over the
fins 104, the CESL 164 over the S/D features 162, the ILD layer 166
over the CESL 164, and the protective dielectric layer 168 over the
ILD layer 166. For example, the operation 216 may etch recesses
into the fins 104 adjacent to the gate spacer 160, and epitaxially
grow semiconductor materials in the recesses. The semiconductor
materials may be raised above the top surface of the fins 104. The
operations 216 may form the S/D features 162 separately for NFET
and PFET devices. For example, the operations 216 may form the S/D
features 162 with n-type doped silicon for NFET devices or p-type
doped silicon germanium for PFET devices. Thereafter, the operation
218 may deposit the CESL 164 and the ILD layer 166 over the S/D
features 162. The CESL 164 may comprise silicon nitride, silicon
oxynitride, silicon nitride with oxygen (O) or carbon (C) elements,
and/or other materials; and may be formed by CVD, PVD, ALD, or
other suitable methods. The ILD layer 166 may comprise
tetraethylorthosilicate (TEOS) oxide, un-doped silicate glass, or
doped silicon oxide such as borophosphosilicate glass (BPSG), fused
silica glass (FSG), phosphosilicate glass (PSG), boron doped
silicon glass (BSG), and/or other suitable dielectric materials.
The ILD layer 166 may be formed by PECVD, FCVD, or other suitable
methods. Subsequently, the operation 218 may etch back the ILD
layer 166 and deposit the protective dielectric layer 168 which may
comprise a nitride such as silicon nitride for protecting the ILD
layer 166 during subsequent etching processes. The operation 216
performs one or more CMP processes to planarize the top surface of
the device 100.
[0055] At operation 218, in a replacement gate process, the method
200 (FIG. 2B) replaces dummy gate stacks with high-k metal gate
stacks 112 having a high-k dielectric layer 108 and a conductive
layer 110, such as shown in FIGS. 16A and 16B. The operation 218
begins by removing the dummy gate structures to form gate trenches
(not shown) between the gate spacers 160 and deposits high-k metal
gate stacks 112 in the gate trenches. The high-k metal gate stacks
112 include the high-k dielectric layer 108 and the conductive
layer 110. The high-k metal gate stacks 112 may further include an
interfacial layer (e.g., silicon dioxide or silicon oxynitride)
(not shown) between the high-k dielectric layer 108 and the fins
104. The interfacial layer may be formed using chemical oxidation,
thermal oxidation, ALD, CVD, and/or other suitable methods. The
materials of the high-k dielectric layer 108 and the conductive
layer 110 have been discussed above with reference to FIGS. 1A-1D.
The high-k dielectric layer 108 may include one or more layers of
high-k dielectric material, and may be deposited using CVD, ALD,
and/or other suitable methods. The conductive layer 110 may include
one or more work function metal layers and a metal fill layer, and
may be deposited using methods such as CVD, PVD, plating, and/or
other suitable processes.
[0056] At operation 220, the method 200 (FIG. 2B) performs further
steps to complete the fabrication of the device 100. For example,
the method 200 may form contacts and vias electrically connecting
the S/D features 162 and the gate stacks 112 and form metal
interconnects connecting various transistors to form a complete
IC.
[0057] Although not intended to be limiting, one or more
embodiments of the present disclosure provide many benefits to a
semiconductor device and the formation thereof. For example,
embodiments of the present disclosure provide a notched gate
structure and a gate fabrication technique that maintains the
uniformity of notched gate structure profiles across a wafer. The
notched gate structure reduces effective gate stack CDs and
enlarges distance from a base of a gate stack to other FETs
features, therefore mitigating possible shorting caused by metal
gate protrusion and increasing a chip yield rate in the edge region
of a wafer. Furthermore, formation of this notched gate structure
can be easily integrated into existing semiconductor fabrication
processes.
[0058] In one exemplary aspect, the present disclosure is directed
to a method. The method includes providing a structure having a
first region and a second region, the first region including a
first channel region, the second region including a second channel
region; forming a gate stack layer over the first and second
regions; patterning the gate stack layer, thereby forming a first
gate stack over the first channel region and a second gate stack
over the second channel region; and laterally etching bottom
portions of the first and second gate stacks by applying different
etchant concentrations to the first and second regions
simultaneously, thereby forming notches at the bottom portions of
the first and second gate stacks. In some embodiments, the applying
of the different etchant concentrations includes applying different
etchant flow rate settings to gas injectors over the first region
and the second region in a plasma processing chamber. In some
embodiments the structure is a semiconductor wafer, the second
region is a center region of the semiconductor wafer and the first
region is a peripheral region of the semiconductor wafer, and the
peripheral region receives a higher etchant concentration than the
center region during the laterally etching of the bottom portions
of the first and second gate stacks. In some embodiments, the
peripheral region receives about 5% to about 20% higher etchant
concentration than the center region during the laterally etching
of the bottom portions of the first and second gate stacks. In some
embodiments, the patterning of the gate stack layer includes
performing an anisotropic etching that forms a passivation layer on
sidewalls of the first and second gate stacks, the passivation
layer having a lower portion thinner than an upper portion. In some
embodiments, the laterally etching of the bottom portions of the
first and second gate stacks includes removing the lower portion of
the passivation layer. In some embodiments, the patterning of the
gate stack layer includes applying a plasma containing HBr and
O.sub.2. In some embodiments, the laterally etching of the bottom
portions of the first and second gate stacks includes applying a
plasma containing HBr. In some embodiments, the plasma containing
HBr is free of O.sub.2. In some embodiments, the structure having a
semiconductor substrate and semiconductor fins protruding from the
semiconductor substrate in both the first and second regions, and
wherein the first and second channel regions are inside the
semiconductor fins. In some embodiments, the first and second
channel regions have a channel length ranging from about 16 nm to
about 240 nm.
[0059] In another exemplary aspect, the present disclosure is
directed to a method. The method includes providing a structure
having a semiconductor substrate and semiconductor fins protruding
from the semiconductor substrate in a first region and a second
region, forming a gate material layer over the semiconductor fins,
etching the gate material layer with a first etchant, thereby
forming a first gate stack in the first region and a second gate
stack in the second region, and etching the first and second gate
stacks with a second etchant, the second etchant having different
concentrations in the first and second regions, thereby forming the
first and second gate stacks with bottom portions narrower than top
portions. In some embodiments, the method further includes
replacing the first and second gate stacks with respective first
and second high-k metal gate stacks. In some embodiments, the first
and second etchants have different material compositions. In some
embodiments, the first etchant is a plasma containing HBr and
O.sub.2 and the second etchant is a plasma containing HBr. In some
embodiments, the etching of the gate material layer includes a
first plasma etching under a first pressure and a first RF power,
and the etching of the first and second gate stacks includes a
second plasma etching under a second pressure and a second RF
power, the second pressure being higher than the first pressure and
the second RF power being higher than the first RF power. In some
embodiments, the second region is at a center of the structure and
the first region is at an edge of the structure, and during the
etching of the first and second gate stacks, the second etchant has
a concentration about 5% to about 20% higher in the first region
than in the second region. In some embodiments, the gate material
layer includes polysilicon or silicon nitride.
[0060] In yet another exemplary aspect, the present disclosure is
directed to a method of semiconductor device fabrication. The
method includes providing a semiconductor wafer; forming a first
plurality of fins in a center region of the semiconductor wafer and
a second plurality of fins in an edge region of the semiconductor
wafer; forming a dielectric layer over the first and second
pluralities of fins; patterning the dielectric layer, thereby
forming a first plurality of dummy gates on the first plurality of
fins and a second plurality of dummy gates on the second plurality
of fins; performing a dry etching process to the first and second
pluralities of dummy gates by applying different etchant flow rates
to the center and edge regions, thereby forming the first and
second pluralities of dummy gates with bottom portions narrower
than top portions; and replacing the first and second pluralities
of dummy gates with respective first and second pluralities of
metal gates, wherein the first and second pluralities of metal
gates have bottom portions narrower than top portions. In some
embodiments, the dry etching process is performed in a plasma
processing chamber with multiple gas injectors having different
etchant flow rate settings over the center region and the edge
region.
[0061] The foregoing outlines features of several embodiments so
that those of ordinary skill in the art may better understand the
aspects of the present disclosure. Those of ordinary skill in the
art should appreciate that they may readily use the present
disclosure as a basis for designing or modifying other processes
and structures for carrying out the same purposes and/or achieving
the same advantages of the embodiments introduced herein. Those of
ordinary skill in the art should also realize that such equivalent
constructions do not depart from the spirit and scope of the
present disclosure, and that they may make various changes,
substitutions, and alterations herein without departing from the
spirit and scope of the present disclosure.
* * * * *